Water-laid sheets containing synthetic fibers



WATER-LMD SHEETS GONTAINING SYNTHETIC FIBERS Filed OG. 28, 1955 M. M. CRUZ Dec. 23, 1969 2 Sheets-Sheet l M. M. cRU 3,485,713

WATER-LAID SHEETS CONTAINING SYNTHETC FIBERS 2 Sheets-Sheet 2 Dec. 23, 1969 Filed OOC. 28. 1966 HANDSHEETS OF CELLULOSE MONOTHIOCARBONATE AFTER DISPERSION (N A TAPP( DISINTIGRATOR FOR DISULFIDE NUMBER OF REVOLUTIONS SHOWN.

2500 REVOLUTIONS 7500 REVOLUTIONS (IX) (IX) (2,500 REVOLUTIONS 20,000 REVOLUTIONS (IX) (IX) FIG. 2.

/NVENTR MAMERTO M. CRUZ @Y M725 m nited States Patent O 3,485,713 WATER-LAID SHEETS CONTAINING SYNTHETIC FlBlERS Mamet-to M. Cruz, Pennington, NJ., assignor to FMC Corporation, New York, NX., a corporation of Delaware Filed Oct. 28, 1966, Ser. No. 590,231 Int. Cl. D21h 5/12 US. Cl. 162-146 10 Claims ABSTRACT F THE DISCLOSURE Cellulose xanthide and cellulose monothiocarbonate disulfide are each formed into fibers having natural selfdispersing and self-bonding properties when made into water-laid sheets; these fibers are produced by passing a cellulose xanthate solution into a spinning bath having a pH of from about l to about 8.5, and contacting the resultant cellulose xanthate fiber with an oxidizing agent at a pH of 1.5 to about 7.5 to convert the fiber to cellulose xanthide; this, in turn, can be oxidized to cellulose monothiocarbonate disulfide by treating the fiber at a temperature of about 6-60 C. with chlorine dioxide.

This invention relates to a method of forming Waterlaid sheets and specifically to the production of waterlaid sheets containing fibers formed from cellulose xanthide and cellulose monothiocarbonate disulfide.

In the production of water-laid sheets, such as paper, from naturally occurring cellulose fibers, e.g. wood pulp, the fibers are subjected to mechanical beating to form a pulp slurry. During this beating operation a microscopic peeling of the individual fibrils at the ends and surfaces of the fibers occurs due to the mechanical action of the beater and the hydrating action of the slurry. The microscope peeling loosens minute, elongated elements, called fibrillae, which make up the structure of the fiber. When this pulp slurry is passed through a fine screen, such that the fibers are deposited in a sheet, the physical properties of the sheet are, to a large extent, dependent on the interlocking of the hydrated fibers and the fibrillae on the fibers during the subsequent drying Stage. Obviously, changes in the paper-making process, including the addition of additives, which affect the fiber-tofiber bonding that develops upon drying, will alter the physical properties of the final paper.

In contrast to naturally occuring cellulose fibers, synthetically produced bers do not form fibrillae during the beating stage as do natural cellulose fibers, and thus do not exhibit the fiber-to-fiber bonding which is characteristic of natural cellulose fibers after being mechanically beaten. Thus, the formation of Water-laid sheets of such synthetic fibers results in a water-laid sheet having very poor sheet strength.

Another difficulty in producing Water-laid sheets from synthetic fibers is that unlike natural cellulose fibers, they are difficult to disperse uniformly in Water. When an aqueous suspension of these fibers is laid down to form a sheet, the fibers tend to agglomerate and result in a nonuniform, poor quality, water-laid sheet. This inability to form uniform, satisfactory, water-laid sheets is particularly aggravated when the synthetic fibers are longer than about Mt".

It is possible to improve the physical properties of such Water-laid sheets by the incorporation of binders. However, such binders are generally undesirable because they require additional processing techniques in the papermaking process. Further, the binding materials reduce the desired porosity of the Water-laid products and in many cases cause undesirable stitfening of the final paper.

ICC

It is an object of the present invention to produce water-laid sheets containing cellulose-derived fibers which have naturally good dispersing and bonding properties.

It is a further object of the present invention to produce novel, cellulose-derived fibers and to dene a process for producing these novel fibers.

These and other objects Will be apparent from the following description.

I have now found a method for making the compounds cellulose xanthide and cellulose monothiocarbonate disulfide into bers that have natural self-dispersing and self-bonding properties when staple lengths of either of these fibers is placed in an aqueous slurry and the slurry is passed through a screen to form a Water-laid sheet; the Water-laid sheet may be made up solely of the above fibers or it may be mixed with nonbonding fibers such as regenerated cellulose or derivatives thereof, polyamides, polyesters, polyolens or bast fibers.

In order to carry out the present invention, fibers of cellulose xanthide or of cellulose monothiocarbonate disulfide are first formed. In brief, this is achieved first by producing cellulose xanthate in a conventional manner. This is carried out by reacting a cellulose product derived from cotton, Wood, etc. with sodium hydroxide and carbon bisulfide in the ratios necessary to produce cellulose xanthate. The resulting cellulose xanthate solution thus obtained is formed into cellulose xanthate filaments by passing the solution through an aqueous, acidic, salt solution as defined hereinafter; the cellulose xanthate filaments are oxidized to filaments of either cellulose xanthide or cellulose monothiocarbonate disulfide as shown in the following reactions:

(1) S S S Il oxidizing [I 1| 2RO-C-SNa RO- -S-S-C-OR (cellulose agent xanthide) (2) S S O O Il l (C102) oxidizing 1| RO-C-S-S-C-OR RO-C-S-S-C-OR agent (cellulose monothio- (cellulose xanthide) carbonate disulfide) where RO refers to -anhydroglucose units of cellulose.

In the reaction to convert cellulose to cellulose xanthate, sodium hydroxide and carbon bisulfide are added to cellulose in mole ratios, respectively, of at least 033:0.15 per mole of cellulose. The reaction is carried out at temperatures of about l0 to about 60 C. in a sealed chamber to prevent the escape of carbon bisulfide. The resulting cellulose xanthate should have a DS (degree of substitution) of at least 0.02. The DS expresses numerically the moles of carbon bisulfide that have reacted with one mole (162 grams) of cellulose.

The above reaction for conversion of cellulose to form a cellulose xanthate solution is conventional in the art and does not form any part of this invention.

In accordance with the present invention the resulting cellulose xanthate solution instead of being spun into conventional regenerated cellulose is spun into filaments of cellulose xanthate by passing the solution through a spinning head having one or more fine openings into an aqueous spinning bath. The bath should contain from about 5 to about 15% by Weight of a salt such as sodium acid phosphate and have a pH of from about 1 to about 8.5. The preferred pH is from about 4.5 to 6. Other salts which can be used in the same manner as sodium acid `phosphate (NaH2PO4) are the salts of phosphoric acid, e.g. Na2HPO4, NH4HPO4, Na3PO4; salts of 0 sulfuric acid, e.g. Nal-1804, NH4HPO4, Na2SO4; alkali metal or alkaline earth halides, c g. NaCl, NaBr, KCl, KI, CaCl2, MgCl2, BaBr2; salts of carbonic acid, e.g.

Na2CO3; salts of organic acids, e.g. sodium acetate, sodium citrate.

While 5 to 15% by weight of the above salts represents the amount normally employed in the spinning bath, larger amounts may be employed up to the solubility limit of the bath. In this stage of the process the xanthate fiber remains as cellulose xanthate without being chemically converted to any substantial degree. The pH of the spinning bath should be carefully controlled to avoid substantially stronger acid baths than those specified above, since too acid a bath will convert the cellulose xanthate to undesired regenerated Cellulose.

The resulting cellulose xanthate filaments produced above are oxidized to cellulose xanthide by means of an oxidizing agent such as iodine or an alkali metal hypochlorite. In practice this is carried out by contacting the cellulose xanthate filaments at a pH of about 1.5 to about 7.5, and preferably at a pH of about 3.5 to 6.5 with the desired oxidizing agent, e.g. iodine or sodium hypochlorite, in an amount sufficient to convert the cellulose xanthate to cellulose xanthide. This may be achieved by passing the xanthate fiber through an initial acid bath, e.g. sulfuric, acetic, hydrochloric, or other suitable organic or inorganic acid, and subsequently passing the fiber through a sodium hypochlorife solution. Alternately, the xanthate fiber may simply be passed through an acidified solution containing the desired oxidizing agent. Suitable oxidizing agents include I2, BrCN, aqueous chlorine, NO or nitrous acid, NO2 or nitric acid, chromic acid, NaBO3, NaOBr, peracetic acid, chlorinated cyanuric acids and salts thereof, persulfate salts, e.g. (NH4)2S2O8, Chloramine-T, NHZCl, O3, H2O2, alkali and alkaline earth metal peroxides, e.g. Na202.

An excess of the oxidizing agent, e.g. the hypochlorite solution, is normally used over the theoretical amount required for conversion of the xanthate groups to the xanthide. When using sodium hypochlorite as the oxidizing agent, it is preferred to employ a molar ratio of sodium hypochlorite to the xanthate group of 1.5 :l to 1.9:1 and to carry out the conversion at a temperature of to 30 C. to avoid decomposition of the xanthate groups.

Conversion of the cellulose xanthide fibers or filaments into cellulose monothiocarbonate disulfide is achieved by treating the cellulose xanthide with chlorine dioxide at a temperature of 0 to 60 C. and at a pH of from about 1 to about 6. It is preferred to carry out the reaction at temperatures of from about 10 to about 30 C. and at a pH of about 3.5 to 4.5, because these conditions minimize loss of chlorine dioxide during the reaction. The chlorine dioxide is employed `preferably in a ratio of about 4 moles of C102 per mole of xanthide group to be converted. Larger amounts of C102 may be added because any excess chlorine dioxide which is not reacted does not ydegrade the anhydroglucose units of the cellulose product.

In accordance with the present invention, the cellulose xanthide or cellulose monothiocarbonate disulfide filaments are cut into desired lengths. In the production of porous paper, where substantially long fibers are desired, the filaments are cut in lengths of from 1A. to 2". The filaments are then dispersed in water to form a suspension, and the suspension is passed through a fine screen to make water-laid sheets of paper in a conventional fashion. On a laboratory scale this is carried out by placing the pulp suspension in a box Whose bottom is made up of a fine screen. The slurry is then permitted to pass through the screen, and the staple length fibers remain on the screen to form the water-laid sheet while the water passes through.

In the practice of the present invention the water-laid sheet may be made up entirely of either cellulose xanthide filaments, cellulose monothiocarbonate disulfide filaments, or mixtures thereof. However, either of these filaments may be mixed with other filaments, such as rayon or rayon acetate, which in themselves have little selfbonding properties, to produce a water-laid sheet having good physical properties. Examples of such other filaments include polyamides such as nylon; polyesters such as Dacron; polyolefins such as polyethylene or polypropylene; and natural vegetable fibers such as ramie, sisalv abaca and magueyl The proportion of cellulose xanthate filaments or cellulose monthiocarbonate disulfide filaments is not critical except that with increasing proportions of the xanthide or monothiocarbonate disulfide fibers increasedbonding strength is obtained.

The invention will now be illustrated by reference to the following drawings.

In the drawings:

FIGURE 1 shows photomicrographs (150x) under partially crossed (34), polarized light, of handsheets of (A) cellulose xanthide,

(B) cellulose monothiocarbonate disulfide, and

(C) a blend of cellulose xanthide and rayon prepared respectively in Examples 3, 4 (Run A) and 6.

FIGURE 2 shows photomicrographs (1X) of handsheets prepared from cellulose monothiocarbonate disulfide fibers made after the fibers were dispersed for:

(A) 2,500, revolutions in a Standard TAPPI distintegrator.

(B) 7,500, revolutions in a Standard TAPPI disintegrator.

(C) 12,500 and revolutions in a Standard TAPPI disintegrator.

(D) 20,000 revolutions in a Standard TAPPI disintegrator.

The handsheets shown in the photomicrographs of FIG- URE 2 were produced in accordance with Example 5.

The following examples are given to illustrate the nvention and are not deemed to be limiting thereof.

EXAMPLE 1 Preparation of cellulose xanthide filaments A freshly prepared cellulose xanthate solution contain ing the equivalent of 9% cellulose and 6% NaOH and having 30.5 CS2 (based on the weight of the cellulose) was prepared such that it had a ball fall viscosity of 28 seconds, and a sodium chloride salt test of 8.0. This deaerated and filtered solution was spun through a spinning head into an aqueous spinning bath containing 12% sodium acid phosphate, 10% sodium sulphate, and having a pH of 4.3-4.7. The spinning speed was 25 meters per minute, and the immersion length was 36". The spinning was carried out in a bath temperature of 30 C. Subsequent to the spinning bath the cellulose xanthate filaments were passed through a second bath containing 3% NaOCl. 15% NagSO., and having a pH of 5.5. In this bath the cellulose xanthate filaments were stretched to a stretch value of 113% and simultaneously were converted to cellulose xanthide filaments. Continuous cellulose xanthide filaments (540 denier filament) were collected in a centrifugal box during the spinning operation and contained a twist of 3 turns per inch. The fibers were washed repeatedly with an acetone-water mixture, given a final-acetone wash and air dried. About 250 grams ot' fiber, dry basis, was o-btained. It had a value of 6% sulfur corresponding to a DS of 0.1.

EXAMPLE 2 Preparation of cellulose monothiocarbonate disulfide One hundred grams of the dry cellulose xanthide fibers produced in Example l were treated with 500 ml. of 2% C102 solution at 25 C. for 45 minutes. The resultant white fibers were then washed 'repeatedly with water, an acetone-water solution, and finally with acetone before being air dried. The resulting fiber product was identified as cellulose monothiocarbonate disulfide, containing 3.7% sulfur, which corresponded to a DS of 0.12. The resultant cellulose monothiocarbonate disulfide fiber weighed 46 grams on a, moisture free basis.

EXAMPLE 3 The continuous filaments of cellulose xanthide produced as set forth in Example l were randomly cut into 1/2 to 2 staple lengths. Thirty grams of these randomly cut fibers were dispersed in 200 ml. `of tap water. The pH of the fiber suspension was adjusted to 8.5 with a dilute NaOH solution. Five ml. of a 5.25% NaOCl solution with a pH of 7.5 was added to the mixture with mild agitation. The suspension was transferred to a proportioner and diluted to 17.9 liters. The mixture was agitated by bubbling air into the proportioner. This suspension was then passed through a fine wire screen to form 8 x 8 Noble and Wood handsheets using a Noble and Wood sheet mold. The water-laid sheets were thenj passed through a felt press and partially dried on a Noble and Wood hotplate at 325 F. for 30 seconds. The dried handsheets were then conditioned and tested in accordance with TAPPI Standard 220m-60. The results of the testing are set forth in Table l. A photomicrograph of a handsheet is illustrated in FIGURE 1(A) of the drawings.

EXAMPLE 4 Run A.-The procedure of Example 3 was repeated except that the continuous filaments of cellulose monothiocarbonate disulfide produced as set forth in Example 2 were used. Further, these fibers were dispersed in a disintegrator for 25,000 revolutions prior to forming handsheets. The resulting dried handsheets were conditioned and tested in accordance with TAPPI Standard 220m-60. The results of the testing are set forth in Table 1. A photomicrograph of a handsheet is illustrated in FIGURE 1(B) of the drawings.

Run B.-ln order to have a basis of comparison, a rayon fiber was cut in the same manner as set forth in Run A and a water-laid sheet made from the cut rayon staple fibers, using the same technique as set forth above in Run A. In the process of making the handsheets, the rayon staple fibers were found difficult to disperse in water. Further, the fibers tended to clump and entangle themselves to form non-uniform sheets in the water-laid sheet making process. The water-laid sheet was tested in the same manner as Run A and the results are set forth in Table l.

results are set forth in Table 2. Photomicrographs of these handsheets are illustrated in FIGURE 2 of the drawings.

TABLE 2 Disintegrator, Revolutions Description of 8 x 8" Dried Handslieet 5 fiber bundles.

20, 000 Completely dispersed.

The procedure of Example 3 was repeated, and handsheets were made from cellulose xanthide filaments cut into 1/2 to 2 staple lengths mixed with 3.0 denier rayon fibers. The handsheets contained a blend of 33% cellulose xanthide fibers and 67% of 3.0 denier rayon fibers (cut to 1/2"). The fiber slurries were dispersed for 2,500 revolutions in a TAPPI disintegrator prior to sheet formation. The sheets showed excellent dispersing properties and good web-forming properties. The sheets had physical properties similar to the sheets produced in Example 3. A photomicrograph of a handsheet is illustrated in FIG- URE l(C) of the drawings.

EXAMPLE 7 The procedure of Example 4 was repeated using a 33% mixture of cut cellulose monothiocarbonate disulfide iibers and 67% cut rayon fibers. The results obtained are similar to those set forth in Example 6 in that the papers of the fibers showed good dispersing properties and good web-forming properties.

What is claimed is:

1. As an article of manufacture, filaments consisting essentially of cellulose monothiocarbonate disulfide.

2. Process of producing a fiber consisting essentially of cellulose xanthide which comprises passing a cellulose xanthate solution through a spinning head, having at least one opening therein, into a spinning bath having a pH of from about l to about 8.5, removing a fiber consisting essentially of cellulose xanthate from said spinning bath,

TABLE l Breaking Length, 1n. Burst Factor Tear Factor Sample Fiber Type Cond. Wet Cond. Wet Cond. Wet

C2 3H3A. 3.0 denier, W cut rayon fibers No measurable strength 02131-43 4.0 denier, to 2" cut cellulose xanthide fibers 2,000 429 15 l2 153 131 C2l3lA3B 3.0 denier, V2 to 2" cut cellulose MTDS fibers l, 930 393 12 12 142 110 As will be seen from Table l the handsheet made up of rayon fiber has substantially no measurable strength, while the cellulose xanthide fibers and cellulose monothiocarbonate disulfide libers all showed appreciable bonding strengths.

EXAMPLE 5 then passed through a felt press `and dried on a Noble and F Wood drum drier. The remaining suspension was then subjected to additional revolutions, and 200 ml. portions were removed and formed into sheets in the manner set forth above at the end of 7,500, 12,500 and 20,000 revolutions. The resulting handsheets were then examined. The

contacting said cellulose xanthate fiber at a temperature of about l0 to about 30 C. with at least a stoichiometric amount of an oxidizing agent selected from the group consisting of iodine, sodium hypochlorite, BrCN, aqueous chlorine, NO, HNOZ, NO2, HNOS, NaBO3, NaOBr, peracetic acid, chlorinated cyanuric acids and salts thereof, ammonium persulfate, H2O2, NH2C1, O3 and alkali and alkaline earth metal peroxides, at a pH of 1.5 to about 7.5, for a period sufficient to convert said cellulose xanthate fiber to cellulose xanthide and recovering a cellulose xanthide fiber from said oxidizing solution.

3. Process of producing a ber consisting essentially of cellulose monothiocarbonate disulfide which comprises passing a cellulose xanthate solution through a spinning head, having at least one opening therein, into a saline spinning bath having a pH of from about l to about 8.5, removing a fiber consisting essentially of cellulose Xanthate from said spinning bath, contacting said cellulose xanthate fiber at a temperature of about l0 to about 30 C. with at least a stoichiometric amount of an oxidizing agent selected from the group consisting of iodine, sodium fiber bundles, mostly 2 long fibers 30 fiber bundles, mostly 2 long fibers.

hypochlorite, BrCN, aqueous chlorine, NO, HNO2, NO2, HNO3, NaBO3, NaOBr, peracetic acid, chlorinated cyanuric acids and salts thereof, ammonium persulfate, H2O2, NH2C1, O3 and alkali and alkaline earth metal peroxides, at a pH of 1.5 to 7.5, for a period sucient to convert said cellulose Xanthate ber to cellulose Xanthide, contacting the resulting cellulose Xanthide fiber with at least stoichiometric amounts of chlorine dioxide at a temperature of from about 0 to about 60 C. for a time suicient to convert said cellulose. Xanthide fiber to cellulose monothiocarbonate disulfide, and recovering as a product a fiber consisting essentially of cellulose monothiocarbonate disulde.

4. Process of claim 2 wherein said spinning bath has a pH of from about 4.5 to 6 and said cellulose Xanthate bers are oxidized at a pH of from about 3.5 to about 6.5.

S. Process of claim 3 wherein said spinning bath has a pH of from about 4.5 to 6 and said cellulose Xanthate fibers are oxidized at a pH of from about 3.5 to about 6.5.

6. Process of producing Water-laid sheets from la- 20 ments having natural self-bonding properties which comprises dispersing laments consisting essentially of a compound selected from the group consisting of cellulose Xanthide and cellulose monothiocarbonate disulfide in water to form a slurry thereof, forming a wet-laid sheet of said filaments by passing said slurry through a screen and recovering a water-laid sheet having good self-bonding properties.

7. The process of claim 6 wherein the compound is cellulose Xanthidc.

8. The process of claim 6 wherein the compound is cellulose monothiocarbonate disulfide.

9. The process of claim 6 wherein said filaments are mixed with a fiber selected from the group consisting of regenerated cellulose, cellulose acetate, polyesters, polyolens, and bast fibers.

10. Process of claim 9 wherein said bers are regenerated cellulose.

References Cited UNITED STATES PATENTS 2,296,857 9/1942 Lilienfeld 264.-.188 X 3,160,552 12/1964 Russell et al 162-177 X 3,304,223 2/1967 Wheeler 162-177 X FOREIGN PATENTS 268,505 2/ 1926 Great Britain.

HOWARD R. CAINE, Primary Examiner U.S. C1. X.R. 

